This invention relates generally to gas turbines, and more particularly, to methods and systems that facilitate reducing NOx (generic for any nitrogen oxide combination) emissions from turbine engines.
At least some known combustors used with gas turbine engines produce NOx emissions as a by-product of the combustion process. Generally, the cause of NOx emissions may be two-fold. First, higher combustion temperatures generated within the combustor facilitate the production and output of NOx emissions. Second, an increased residence time, or time required for fuel and air to mix within the combustor also facilitates increased NOx emissions.
To facilitate reducing combustor temperatures and residence times, at least some known combustors include dilution holes formed in the combustor liner. Specifically, the dilution holes are positioned to discharge dilution air into the combustion chamber to facilitate increasing the rate of mixing of fuel and air within the combustor. Moreover, the dilution air facilitates reducing the combustion temperature while maintaining desired combustion levels.
Generally, because of the positioning and/or orientation of dilution holes within the combustor liner, at least some known combustors which satisfy current emissions standards, as specified by the International Civil Aviation Organization (ICAO) Committee on Aviation Environmental Protection (CAEP), may not meet more stringent standards. For example, at least some known engines that are capable of meeting current CAEP standards (that are effective as of Dec. 31, 2003), may not satisfy future CAEP standards that come into effect after Dec. 31, 2007. Specifically, at least some known engines include dilution holes positioned only at a downstream end of the combustor. However, within such combustors, dilution air may not reduce residence times and/or combustion operating temperatures near a forward end of the combustion chamber, where NOx emissions may be generated.